Apparatus and method of non-invasive cerebrovascular autoregulation monitoring

Abstract

A non-invasive method for monitoring of cerebrovascular blood flow autoregulation state includes sensing intracranial blood volume waves, filtering a slow wave, respiratory wave, and pulse wave informative components from said intracranial blood volume waves, filtering slow wave and respiratory wave reference components from the pulse wave envelope, calculating a first phase shift between said slow wave informative component and said slow wave reference component, calculating a second phase shift between said respiratory wave informative component and said respiratory wave reference component, and calculating the index of evaluation of the status of cerebral autoregulation state (ICAS) from said first phase shift and said second phase shift.

1. A method for non-invasively monitoring cerebrovascular autoregulation state comprising the steps of:
 obtaining intracranial blood volume waves; 
 filtering a first informative wave from the intracranial blood volume Waves, said first informative wave comprising an intracranial blood volume slow wave; 
 filtering a second informative wave from the intracranial blood volume waves, said second informative wave comprising an intracranial blood volume respiratory wave; 
 filtering a primary reference wave from the intracranial blood volume waves; 
 demodulating the primary reference wave into a reference wave envelope; 
 filtering a first reference wave from the reference wave envelope; 
 filtering a second reference wave from the reference wave envelope; 
 calculating a first phase shift between said first informative wave and said first reference wave; 
 calculating a second phase shift between said second informative wave and said second reference wave; 
 calculating in a processor an index of evaluation of the status of cerebral autoregulation state from said first phase shift and said second phase shift; and 
 comparing in a processor said index of evaluation of the status of cerebral autoregulation state to a predetermined index threshold value to determine cerebrovascular autoregulation state. 
 
     
     
       2. The method of  claim 1  wherein said index of evaluation of the status of cerebral autoregulation state is calculated using the following formula:
   ICAS=cos(π− a 1* PS 1− a 2* PS 2)
 
 
       wherein PS 1  is said first phase shift and PS 2  is said second phase shift and where a 1  and a 2  are weighting factors. 
     
     
       3. The method of  claim 2  wherein the value of weighting factor a 1  is 0.61 and the value of weighting factor a 2  is 0.42. 
     
     
       4. The method of  claim 1  wherein said primary reference wave comprises an intracranial blood volume pulse wave. 
     
     
       5. The method of  claim 1  wherein said first reference wave comprises a slow wave from the pulse wave envelope. 
     
     
       6. The method of  claim 1  wherein said second reference wave comprises a respiratory wave from the pulse wave envelope. 
     
     
       7. The method of  claim 1  further comprising the step of determining said cerebrovascular autoregulation state is absolutely intact when said calculated ICAS is close to −1.0. 
     
     
       8. The method of  claim 1  further comprising the step of determining said cerebrovascular autoregulation state is absolutely impaired when said calculated ICAS is close to +1.0. 
     
     
       9. A method for non-invasively monitoring cerebrovascular autoregulation state comprising the steps of:
 non-invasively obtaining intracranial blood volume waves; 
 filtering a slow wave informative component from said intracranial blood volume waves, said slow wave informative component comprising an intracranial blood volume slow wave; 
 filtering a respiratory wave informative component from said intracranial blood volume waves said respiratory wave informative component comprising an intracranial blood volume respiratory wave; 
 filtering a pulse wave component from said intracranial blood volume waves; 
 demodulating said pulse wave component into a pulse wave envelope; 
 filtering a slow wave reference component from the pulse wave envelope; 
 filtering a respiratory wave reference component from the pulse wave envelope; 
 calculating a first phase shift between said slow wave informative component and said slow wave reference component; 
 calculating a second phase shift between said respiratory wave informative component and said respiratory wave reference component; 
 calculating in a processor the index of evaluation of the status of cerebral autoregulation state from said first phase shift and said second phase shift; and 
 comparing in a processor said index of evaluation of the status of cerebral autoregulation state to a predetermined index threshold value to determine cerebrovascular autoregulation state. 
 
     
     
       10. The method of  claim 9  wherein said index of evaluation of the status of cerebral autoregulation state is calculated using the following formula:
   ICAS=cos(π− a 1* PS 1− a 2* PS 2)
 
 
       wherein PS 1  is said first phase shift and PS 2  is said second phase shift and where a 1  and a 2  are weighting factors. 
     
     
       11. The method of  claim 10  wherein the value of weighting factor a 1  is 0.61 and the value of weighting factor a 2  is 0.42. 
     
     
       12. The method of  claim 9  further comprising the step of determining said cerebrovascular autoregulation state is absolutely intact when said calculated ICAS is close to −1.0. 
     
     
       13. The method of  claim 9  further comprising the step of determining said cerebrovascular autoregulation state is absolutely impaired when said calculated ICAS is close to +1.0. 
     
     
       14. An apparatus for non-invasively monitoring cerebrovascular autoregulation state comprising:
 a device for obtaining intracranial blood volume waves and generating a blood volume output signal; 
 a first slow wave filter connected to said device for receiving the blood volume output signal, filtering the blood volume output signal, and generating a slow wave informative signal from said blood volume output signal, said slow wave informative signal comprising an intracranial blood volume slow wave; 
 a first respiratory wave filter connected to said device for receiving the blood volume output signal, filtering the blood volume output signal, and generating a respiratory wave informative signal from said blood volume output signal, said respiratory wave informative signal comprising an intracranial blood volume respiratory wave; 
 a pulse wave filter connected to said device for receiving the blood volume output signal, filtering the blood volume output signal, and generating a pulse wave reference signal; 
 an envelope detector connected to said pulse wave filter for receiving said pulse wave reference signal, for demodulating said pulse wave reference signal into a pulse wave envelope, and generating a pulse wave envelope signal; 
 a second slow wave filter connected to said envelope detector for receiving the pulse wave envelope signal, filtering the pulse wave envelope signal, and generating a slow wave reference signal; 
 a second respiratory wave filter connected to said envelope detector for receiving the pulse wave envelope signal, filtering the pulse wave envelope signal, and generating a respiratory wave reference signal; 
 a first phase shift monitor connected to the first slow wave filter for receiving the slow wave informative signal and the second slow wave filter for receiving the slow wave reference signal, determining the phase shift between the slow wave informative signal and the slow wave reference signal, and generating a first phase shift value output; 
 a second phase shift monitor connected to the first respiratory wave filter for receiving the respiratory wave informative signal and the second respiratory wave filter for receiving the respiratory wave reference signal, determining the phase shift between the respiratory wave informative signal and the respiratory wave reference signal, and generating a second phase shift value output; and 
 a processor for receiving the first phase shift value output from the first phase shift monitor and the second phase shift value output from the second phase shift monitor, calculating an index of evaluation of the status of cerebral autoregulation state, said processor also having a stored predetermined index threshold value, and comparing said index of evaluation of the status of cerebral autoregulation state value with said index threshold value to determine the status of cerebrovascular autoregulation state. 
 
     
     
       15. The apparatus of  claim 14  wherein said device is a non-invasive measurement device. 
     
     
       16. The apparatus of  claim 14  wherein said device is an ultrasonic “time-of-flight” measurement device. 
     
     
       17. The apparatus of  claim 14  wherein said first slow wave filter and second slow wave filter comprise a bandpass filter having a bandwidth of approximately 0.008 Hz to 0.033 Hz. 
     
     
       18. The apparatus of  claim 14  wherein said first respiratory wave filter and said second respiratory wave filter comprises a bandpass filter having a bandwidth of approximately 0.1 Hz to 0.35 Hz. 
     
     
       19. The apparatus of  claim 14  wherein said pulse wave filter comprises an adaptive bandpass filter having a bandwidth ranging from approximately the frequency of the first harmonic of the pulse waves to the frequency of the fifth harmonic of the pulse waves. 
     
     
       20. The apparatus of  claim 14  wherein said processor calculates the index of evaluation of the status of cerebral autoregulation state from the following formula:
   ICAS=cos(π− a 1* PS 1− a 2* PS 2)
 
 
       wherein PS 1  is said first phase shift and PS 2  is said second phase shift and where a 1  and a 2  are weighting factors. 
     
     
       21. The apparatus of  claim 20  wherein the value of weighting factor a 1  is 0.61 and the value of weighting factor a 2  is 0.42.